duplex stainless steel

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I didn’t know much about duplex stainless steel before, but I finally know it after collecting it. I hope everyone will not be as confused as I was before. The so-called duplex stainless steel means that in its solid solution structure, the ferrite phase and the austenite phase account for approximately half each. Generally, the content of the minor phase needs to reach 30%. In the case of low C content, the Cr content is 18%~28% and the Ni content is 3%~10%. Some steels also contain alloying elements such as Mo, Cu, Nb, Ti, and N. This type of steel has the characteristics of both austenitic and ferritic stainless steel. Compared with ferrite, it has higher plasticity and toughness, no room temperature brittleness, and significantly improved intergranular corrosion resistance and welding performance. At the same time, it also maintains the 475°C brittleness of ferritic stainless steel, high thermal conductivity, and superplasticity. Compared with austenitic stainless steel, it has high strength and significantly improved resistance to intergranular food and chloride stress corrosion. Duplex stainless steel has excellent pitting corrosion resistance and is also a nickel-saving stainless steel. Performance Characteristics of Duplex Stainless Steel Due to the characteristics of the two-phase structure, through correct control of chemical composition and heat treatment process, duplex stainless steel has the advantages of both ferritic stainless steel and austenitic stainless steel. It combines the excellent toughness and weldability of austenitic stainless steel with ferritic stainless steel. The combination of high strength and chloride stress corrosion resistance has enabled duplex stainless steel to develop rapidly as a weldable structural material. Since the 1980s, it has become a steel type alongside martensitic, austenitic and ferritic stainless steel. Duplex stainless steel has the following performance characteristics: (1) Molybdenum-containing duplex stainless steel has good chloride stress corrosion resistance under low stress. Generally, 18-8 type austenitic stainless steel is prone to stress corrosion cracking in neutral chloride solutions above 600C. Heat exchangers, evaporators and other equipment made of this type of stainless steel in industrial media with trace amounts of chloride and hydrogen sulfide are prone to stress corrosion cracking, while duplex stainless steel has good resistance. (2) Molybdenum-containing duplex stainless steel has good pitting corrosion resistance. When having the same pitting resistance equivalent value (PRE=Cr%+3.3Mo%+16N%), the critical pitting potential of duplex stainless steel and austenitic stainless steel are similar. The pitting corrosion resistance of duplex stainless steel and austenitic stainless steel is equivalent to AISI 316L. The pitting and crevice corrosion resistance of high-chromium duplex stainless steel containing 25% Cr, especially nitrogen, exceeds AISI 316L. (3) It has good resistance to corrosion fatigue and wear and corrosion. Under the conditions of certain corrosive media, it is suitable for making power equipment such as pumps and valves. (4) Good comprehensive mechanical properties. It has high strength and fatigue strength, and its yield strength is twice that of 18-8 austenitic stainless steel. The elongation in the solid solution state reaches 25%, and the toughness value AK (V-shaped notch) is above 100J. (5) The weldability is good and the tendency of hot cracking is small. Generally, no preheating is required before welding, and no heat treatment is required after welding. It can be welded with dissimilar types such as 18-8 austenitic stainless steel or carbon steel. (6) The hot processing temperature range of duplex stainless steel containing low chromium (18% Cr) is wider than that of 18-8 austenitic stainless steel, and its resistance is smaller. It can be directly rolled to produce steel plates without forging. Duplex stainless steel containing high chromium (25%Cr) is slightly more difficult to heat process than austenitic stainless steel, and can produce products such as plates, tubes and wires. (7) The work hardening effect is greater than that of 18-8 type austenitic stainless steel during cold working. In the early stages of deformation of tubes and plates, greater stress needs to be applied to deform. (8) Compared with austenitic stainless steel, it has a large thermal conductivity and a small linear expansion coefficient, and is suitable for use as linings for equipment and for the production of composite panels. It is also suitable for making the tube core of heat exchangers, and its heat transfer efficiency is higher than that of austenitic stainless steel. (9) High-chromium ferritic stainless steel still has various brittleness tendencies and should not be used in working conditions above 3000C. The lower the chromium content in duplex stainless steel, the less harmful brittle phases such as σ are. This post was last edited by QXZ-1966 on 2008-8-17 15:03 ]